To ensure security, it is crucial to take into account finite statistical fluctuations and uncertainties during operation. A vital step for all QKD protocols is to use the transmitted data to estimate parameters, e.g. such as the quantum bit error (QBER), yields from vacuum and single photon emissions, and phase errors [1]}, [2]}, [3]}. In practical use, the transmission window (or integration time) is finite and will be predetermined or limited due to operational considerations such as key refresh tempo or latency. Finite statistical effects can lead to sharp cutoffs in the positive secret key region as a function of channel loss and background count, thus selection of block accumulation lengths and integration times should be balanced against operational requirements.
